Pretreatment of metal bearing surfaces



Patented Dec. 16, 1941 7 PRETREATMENT OF summons METAL BEARING George L. Neely and Victor .M. Kostainsek, Berkeley,"Calif., assignors to Standard Oil Company of California, San Francisco, Calif., a corpora tion of Delaware No Drawing. Application May 18, 1940,

7 Serial No. 336,008

I Claims.

This invention relates to pretreated bearing surfaces and to the method of producing the same, particularly to provide a pretreated bearing surface having improved wear-in characteristics and protected from oxidation orv rusting. This invention is particularly directed to an improvement over that invention disclosed in the co-pending application of Farrington, et al., entitled Treatment of metallic frictional'surfaces" filed Ocwber 19, l938, Serlal No. 235,811.

In the pretreatment of metal bearing or wearing surfaces in order to increase the ability of such surfaces to immediately accommodate high loads without danger of initial failure, processes have now been resorted to of treating such surfaces in order to form on the wear-receiving or bearing surfaces of the ferrous metal bearing elements a sulphide film accompanied with pitting of the surface to produce a multiplicity of lubricant-receiving recesses upon such surfaces.

after contained detailed description of a preferred embodiment of our invention.

The bearing surfaces when so treated have been 7 found to be extremely susceptible to oxidation or rusting with the result that the said elements produce a very unattractive appearance which is detrimental to the sales of such articles, particu: larly when it is necessary to retain the materials in stock or to hold the same for a period of time for use or forsale as replacement parts.

.It is therefore an object of this invention to provide a method of the pretreatment of metal bearing surfaces in order to increase the ability 'of such surfaces to take initial loads without failure and which method also provides for the treatment of the said bearing elements to prevent oxidation or rusting of the film or surface so treated.

Another object of this invention is to provide a method of pretreatlng ferrous metal hearing or wearing surfaces in order to increase the ability of such surfaces to withstand initial extreme pressure loads and which method also includes treatment of such surfaces with a chromateof an alkaline earth metal to prevent oxidation or rusting of the, said treated surface or the film produced upon such surface by the said pretreatment.

Another object of this invention is'to provide a pretreated metal bearing or wearing element the hearing or wearing surface of which is characterized byhaving formed thereon or therein an iron sulphidefllm and furthercharacterized by having its surface pitted and by having upon its surface a coating of an alkali chromate.

.Other objects and advantages of ourinvention it is believed will be apparent from the herei October 17, 1938, for

In accordance with our invention, the ferrous metal hearing or wearing member is first treated to enhance its ability to carry initial loads without failure under extreme pressure by reacting the said bearing surface with a chemical reagent capable of reacting with the ferrous metal of the surface to produce an iron sulphide film upon the surface. The reaction of the ferrous metal ofthe surfa'ce'and the chemical reagent is preferably carried on under suchconditions and for such period of time as will permit the said chemical reagent to selectively etch or pit the surface by selective reaction between the component elements of the surface and the chemical reagent utilized.

Ferrous metal bearing surfaces are usually composed of steel or cast iron or alloys. Chemical reagents which will react with such surfaces to form iron sulphide coatings generally selectively act upon such surfaces particularly with the free ferrite iron in preference to the combined iron orferrous metal of such a surface with the result that the surface is pitted selectively over the area treated, leaving a multiplicity of fine pits or recesses in the surface. The reaction is also and within the pits or recesses formed a deposit or film of iron sulphide. Both the iron sulphide film so produced and the pitting of the surface enhance the ability of carry initial extreme pressure loads without failure. This is as set forth in the co-pending application of Neely, et al., Serial No. 235,542, flied Pretreated bearing surface and method of producing the same."

In accordance with the invention, the pretreated ferrous metal bearing surface is, after thepretreatment, preferably washed or treated to remove any loosely adhering material. The treated surface is next dipped in an alkali chromate solution and allowed to remain in such solution for such period of time as may be required to produce a film or coating of alkali chromate over the bearing surface or the film or coating of iron posited upon the surface.

We have found that the chromate coating or film upon does not decrease or increase the effectiveness of formation of this alkali the previous pretreatment but does effectively retard, and prevent rusting or oxidation of the sur face orthe sulphide film orcoating previously formed on the surface. Any suitable meth d to produce upon the surface the 7 treated surface to method embodying thissulphide previously dethe said surface of pretreatment of the bearing surface to produce the iron sulphide film or coating may be resorted to as, for example, any of those methods disclosed in the co-pending applications hereinabove referred to such as the treatment by hydrogen sulphide 88- or active sulphur in any form. The preferred method, however, is to treat the surface in an alkali sulphur bath as, for example, by dipping the ferrous metal surface in a treating solution made up, for example, of 1,000 grams of 47% NaOH solution to which there is added 50 grams of sulphur. The mixture thus produced is heated to a temperature of about 265 F. and stirred until the sulphur is dissolved in the solution and the solution becomes clear. The ferrous metal bearing surface as, for example, any previously machined bearing surface such as a bearing cup, piston rings, cylinder liners, gears, or any other ferrous metal bearing surface, is then immersed in the solution thus prepared for a period of time and at an elevated temperature sufficient to form upon the surface iron sulphide to produce a dual break coating. Any .other suitable method of forming the iron sulphide film, however, may be resorted to and of course different concentrations of alkali sulphur solution may be employed and other alkali hydroxides may be substituted for the sodium hydroxide above specified.

' Following the formation of the iron sulphide film upon the ferrous metal surface, the surface is washed preferably in warm water to cleanse the same to remove any loosely adhering iron sulphide or other foreign matter from the sur-v face. The cleansed surface as thus produced bearing the iron sulphide coating and which is preferably etched during the process of formation of the coating is then dipped into a solution of alkali chromate ranging anywhere from 1% to alkali chromate to produce upon the surface an alkali chromate film or covering. The particular example of this treatment found'suitable is an alkali chromate treating bath which comprises, for example, 1% to 10% of sodium chromate in water.

A surface having this combined treatment has its resistance to rusting or oxidation increased many fold as compared with a surface treated with alkali sulphur solution alone. We have found that this increased resistance to rusting or oxidation maybe sufficient to avoid the necessity for application of oil or grease to the surface prior to shipment of they treated ferrous metal machine elements.

Tests of the resistance of such combined treated surfaces to the effects of rusting or oxidation are shown in the following table. In these tests previously machined bearing cups were employed. The tests show, as, for example, Test No. l, the rusting effect produced upon the treated and untreated surfaces by -minute interval sprays upon the surfaces of a 0.2% salt (NaCl) solution where twenty such spray applications were made upon the surfaces. 7

Test No. 2 differs only from Test No. 1 in the fact that eight such sprays were utilized with the intervals of time between the sprays l-hour rather than 15-minutes. The extent of the sprays with salt solutions in each case was sufficient to completely cover the surfaces with the salt solution but insufiicient to produce dripping or running of the solution off from the surfaces. These tests are:

SALT SPRAY 'rnsr 1(20 sprays of 2% salt solution at 15-minute intervals) NEW curs Treatment Busting None. Excessive. 17 sodium chromate Partial. i sodium chromate None. 4

TREATED CUPS None Excessive. 1% sodium chromate Partial. 10% sodium chromate None.

SALT SPRAY rnsr 2 --(8 sprays of .2% salt solution at I-hour intervals) NEW CUPS Treatment Busting None .1. Excessive.

TREATED CUPS None Excessiveg, 1%sodium chromate None.

face of ferrous metal comprising contacting the said surface with an aqueous solution containing an hydroxide of an alkali metal containing dissolved sulphur, washing the surface so treated, and then contacting said surface with an aqueous solution of an alkali chromate.

3. A method of pretreatment of a bearing surface of ferrous metal, comprising the pretreatment of said surface with an active sulphur containing chemical reagent to form an iron 'sulphide film on said surface, and to pit the surface, cleaning the surface so treated of foreign matter, and then contacting said surface with an aqueous solution of an alkali chromate.

4. A pretreated bearing surface of ferrous metal characterized in that there is an iron film on said surface, the film consisting of the ferrous metal of the surface and a sulphide radical reacted with an alkali chromate.

5. A pretreated bearing surface of ferrous metal characterized in that its bearing area is pitted from the surface and has a film thereon, the film being a reaction product of the ferrous metal of the surface, a sulphide radical, and an alkali chromate. 1

* GEORGE L. NEELY.

VICI'OR M. KOSTAINSEK. 

